Italians entered the polling booths at 8 am (7am Irish time) today for a general election that could unseat Prime Minister Silvio Berlusconi after five years of economic stagnation.
Voters made a brisk start, lining up outside polling stations to be among the first to place their ballots in a two-day election which could see the return to power of Romano Prodi, leader of a wide centre-left coalition.
Opinion polls have not been published in two weeks, but Mr Prodi has led Mr Berlusconi for the past two years after returning to Italian politics from a five-year stint as president of the European Commission.
Mr Berlusconi, the US government's strongest ally in continental Europe and Italy's richest man, still hopes his promises of tax cuts will swing a surprise victory. But even he spoke of possible defeat in the final days of campaigning.
If poll forecasts are borne out, power will pass from the flamboyant Mr Berlusconi to the mild-mannered Mr Prodi who promises tax breaks for Italian companies and to withdraw troops from Iraq quickly.
Polls were due to remain open until 10 pm today and then open again tomorrow from 7 am to 3 pm. Exit polls will be released minutes after that, with the official results likely to be clear in the late evening.
The election follows the most acrimonious campaign in decades, with Mr Berlusconi using offensive language against centre-left voters and Mr Prodi comparing the prime minister to a drunk.
In one of his tirades against Communists, the prime minister sparked a diplomatic incident with China by telling voters that under Mao Zedong the Chinese Communists boiled babies to use as fertiliser.
Whoever wins will inherit the unenviable task of cutting the world's third-largest debt pile while trying to breathe new life into a struggling economy that grew an average of 0.6 per cent a year under Mr Berlusconi.
Mr Prodi, if elected, would also need to manage a disparate coalition, ranging from die-hard Communists to centrist Roman Catholics, that was united during the campaign mostly by a dislike of Mr Berlusconi.
Among their plans is "conflict of interest" legislation that would force Mr Berlusconi to choose between politics and his immense financial interests stretching from television to film, books, magazines and one of Italy's top soccer teams, AC Milan.
A new voting system rushed into law in December also means that whoever wins is likely to enjoy a smaller parliamentary majority than the outgoing administration, especially in the Senate, which has a key role in passing legislation.
That has raised fears of a return to the "revolving-door" leadership which Mr Berlusconi, elected in 2001, ended by becoming the head of Italy's longest serving post-war government.
There have been 60 administrations since World War Two and coalition instability often brought down governments within their first year of office.
If Mr Prodi's bloc wins the ballot, relations between Rome and Washington will likely become more complicated.
While no one expects a 180-degree shift in foreign policy under Mr Prodi, analysts say he would reverse Mr Berlusconi's priorities, putting Europe rather than the United States first.
Whatever the result, political analysts expect it to take at least a month before a new government can be formed.